1. Field of the Invention
The present invention relates to a parking brake apparatus for applying a brake force to wheels of a parked vehicle. More particularly, the present invention is related to an electrically operated parking brake apparatus for applying the brake force to the wheels through the driving force of an electric motor without relying upon the force applied by the hand or foot of a driver.
2. Description of the Related Art
JP-A-2000-309255 discloses an electrically operated parking brake apparatus with a screw mechanism having in turn a screw-threaded shaft adapted to be rotationally driven by an electric motor, and a nut member adapted to mesh with the screw-threaded shaft. When the screw-threaded shaft is rotated, the nut member is moved along the screw-threaded shaft, whereby a brake operating force is transmitted to wheel brakes via cables connected to the nut member.
When two wheel brakes are put in operation by driving two cables with a single electrically operated parking brake apparatus, it is known to use an equalizer rotatably supported at a central portion thereof by a support shaft and having cables connected to ends thereof. In the electrically operated parking brake apparatus disclosed in JP-A-2000-309255, the equalizer is provided at a position which is situated away from the screw mechanism, and the movement of the nut member of the screw mechanism is transmitted to the equalizer via two slide rods and a cable so that the brake operating force is uniformly divided at the equalizer for transmission to the two wheel brakes via two cables. Then, the two slide rods situated facing each other across the screw-threaded shaft are connected to the nut member such that the reaction force of the brake operating force is not applied to the nut member and the screw-threaded shaft as an unbalanced load.
In the related art electrically operated parking apparatus described above, however, since the nut member and the equalizer are connected to each other via the two slide rods and the cable, the construction of the parking apparatus is complicated because the number of components is increased and also the size of the apparatus is enlarged.
The present invention was made in view of the aforementioned problems in the related art, and an object of the invention is to provide an electrically operated parking brake apparatus which includes a smaller number of components and hence is simple in construction and small in size, and which can prevent an unbalanced load from being applied from the equalizer to the screw mechanism.
With a view to attaining this object, according to the invention, an electrically operated parking brake apparatus, includes:
a pair of transmission members for transmitting a brake operating force to wheel brakes;
an electric motor;
a screw mechanism including a screw-threaded shaft adapted to be rotationally driven by the electric motor, and a nut member meshing with the screw-threaded shaft, the nut member being movable along the screw-threaded shaft by the rotation of the screw-threaded shaft;
an equalizer having connecting portions connecting the pair of transmission members; and
a pair of support shafts disposed at positions facing each other across the screw-threaded shaft for swingably supporting the equalizer on said nut member,
wherein an axis of the pair of support shafts substantially passes through a center of the screw-threaded shaft, and a line connecting the connecting portions of the equalizer substantially passes through the center of the screw-threaded shaft.
According to the above construction, since the axis of the pair of support shafts provided at the positions facing each other across the screw-threaded shaft for swingably supporting the equalizer on the nut member passes through the center of the screw-threaded shaft, the generation of an unbalanced load is prevented which attempts to bend the screw-threaded shaft in a direction normal to a plane containing the axis of the pair of support shafts. In addition, since the line connecting the portions where the pair of transmission members are connected to the equalizer passes through the center of the screw-threaded shaft, the generation of an unbalanced load is prevented which attempts to bend the screw-threaded shaft in a direction normal to a plane containing the line connecting the portions where the pair of transmission members are connected to the equalizer. Thus, the increase in the number of components and enlargement of the size of the parking brake apparatus can be avoided, and the smooth operation of the screw mechanism can be ensured by preventing the generation of an unbalanced load which is applied to the screw-threaded shaft.
Note that Bowden cables 13, 13, a ball screw mechanism 49, and an upper support shaft 51 and a lower support shaft 52 described in an embodiment of the invention correspond to the transmission members, the screw mechanism and the support shafts of the invention, respectively.